Equity-Based Compensation (Summary Of Outstanding Performance Share Awards / Restricted Stock Units) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Performance shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested shares outstanding at January 1, Shares	154,594
Granted (in shares)	85,028	77,767
Forfeited (in shares)	(2,596)
Unvested shares outstanding at September 30, Shares	237,026
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 50.54
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 34.24	$ 55.84
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 44.99
Unvested shares outstanding at September 30, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 44.76
Aggregate Intrinsic Value	$ 8,657
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested shares outstanding at January 1, Shares	36,359
Granted (in shares)	19,725
Vested (in shares)	(1,290)
Forfeited (in shares)	(1,504)
Unvested shares outstanding at September 30, Shares	53,290
Unvested shares outstanding at January 1, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 35.60
Granted, Weighted Av.g Exercise Price (in dollars per share)	$ 31.38
Vested, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 33.27
Forfeited, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 33.36
Unvested shares outstanding at September 30, Weighted Avg. Grant Date Fair Value (in dollars per share)	$ 34.16
Aggregate Intrinsic Value	$ 1,991